The present invention relates to regulated power sources and more particularly to a DC-to-DC converter for providing simpler and less costly isolated power source regulation.
A variety of converter circuits are known in the prior art which are capable of providing DC voltage and current regulation. Typically, the converters have a variety of configurations including the push-pull type, the up-converter and the down-converter. While each of the known devices provide inherent benefits, one of the biggest disadvantages is the complexity of the structures and the regulation and control needed to operate the circuits.
In typical converter circuits, at least two active switches are required in the input circuit to provide switching and maintain symmetry at the transformer. The circuits may be operated in the current-fed or voltage-fed mode, but, in any event, often require specific and detailed regulating circuits to control the output signals. As would be expected, the use of two active switches, in addition to creating a more complex structure, results in a device which may still have non-symmetrical characteristics because of differences in the two switches. As a result, various filtering and switching techniques must be employed to provide proper operation and produce wave-forms of an acceptable shape and magnitude.
In most cases, prior art push-pull and up- or down-converters suffer from several additional disadvantages. In the push-pull converters, there is usually dead time regulation when current or voltage is not being supplied to the output circuit. For low and high line regulation in such structures, larger output filters, high current diodes and high current transformers are required for sustained operation. Likewise, during low line conditions, peak clippers may be required to limit the high energy pulses which occur when the transformer comes out of saturation. Examples of a typical push-pull converter configuration and a description of its operation can be found by reference to U.S. Pat. No. 3,938,024.
In up-converters the maximum efficiency is usually attained only at high line voltage inputs. Additionally, up-converters normally provide a discontinuous output current and require more elements to provide the regulation. Down-converters on the other hand, generally provide a continuous output current over the entire regulation range but, again, maximum efficiency is only obtained at low line input. In down-converters, multiple outputs are not well coupled, there is no inherent current limiting by the circuits and more parts are required, thereby rendering the circuit more complex.
In current technology systems, there is an increasing demand for more inexpensive and well-regulated power supplies capable of providing output isolation and regulation for multiple taps from a single input supply source. In avionics systems in particular, it is important that well-regulated voltage and current outputs are provided over wide ranges of input voltage variations and transients. The regulation is particularly required to avoid damage to extremely sensitive electronic components and circuits and to lessen the cost and space requirements of the power supplies needed to drive increasingly complex circuits.
Accordingly, the present invention has been developed to overcome the shortcomings of the above known and similar techniques and to provide a more effective, efficient and less complex power supply for use in a variety of electronic systems.